US4794255A - Absorption analyzer - Google Patents

Absorption analyzer Download PDF

Info

Publication number
US4794255A
US4794255A US06/935,301 US93530186A US4794255A US 4794255 A US4794255 A US 4794255A US 93530186 A US93530186 A US 93530186A US 4794255 A US4794255 A US 4794255A
Authority
US
United States
Prior art keywords
gas
cell
detector
concentration
ingredient
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
US06/935,301
Other languages
English (en)
Inventor
Kimio Miyatake
Takao Imaki
Kenji Takeda
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Horiba Ltd
Original Assignee
Horiba Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Horiba Ltd filed Critical Horiba Ltd
Assigned to HORIBA, LTD. reassignment HORIBA, LTD. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: IMAKI, TAKAO, MIYATAKE, KIMIO, TAKEDA, KENJI
Application granted granted Critical
Publication of US4794255A publication Critical patent/US4794255A/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Images

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/37—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using pneumatic detection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis

Definitions

  • the present invention relates to an absorption type gas analyzer using infrared rays, ultraviolet rays and the like.
  • an absorption type gas analyzer for example an infrared gas analyzer
  • the absorption of infrared rays incident upon the inside of a cell from a light source by a sample gas contained in the cell is measured to determine the concentration of an ingredient gas contained in the sample gas.
  • This absorption type gas analyzer is fundamentally based on Lambert-Beer's law. That is to say, provided that an intensity of the incident ray is I o , in a cell having a length l, an absorptivity constant K (the constant determined by a measuring-wave length and an object to be measured), and a gas-concentration being C, the intensity of the transmitted ray I is expressed by the following equation:
  • the relation between the concentration of an ingredient gas to be measured and the output of the transmitted light has a larger curvature with an increase of the concentration of an ingredient gas to be measured, as shown in FIG. 2.
  • the cell length is reduced when the concentration of an ingredient gas to be measured is high while the cell length is increased when the concentration of an ingredient gas to be measured is low.
  • a prior art absorption analyzer in which the cell length is changed in correspondence with the concentration of an ingredient gas to be measured in a sample gas, is disclosed in for example Japanese Utility Model Publication No. 49-25349.
  • a prior art device a plurality of cells are arranged in series between a light source and a detector and the cells to be used are changed in correspondence to the cocentration of the ingredient gas to be measured in a sample gas.
  • this prior art device has exhibited disadvantages in that since the cells are arranged in series, the analyzer must be large-sized and overly long as a whole, and a troublesome operation is required in order to change the cell-length in correspondence to the concentration of the ingredient gas to be measured.
  • the provision of an interference filter sideways a light source is disclosed in the above-described Japanese Patent Publication, merely an influence of an interference spectrum upon the measurement is eliminated by previously removing an interference spectrum band overlapping on an absorption spectrum band of an ingredient gas to be measured, but other effects are not achieved.
  • An absorption analyzer comprises at least one light source, at least one gas cell and a detector for determining the absorption of the light emanating from said light source and passing through said gas cell and is characterized in that a gas filter is provided in the optical path between said light source and said detector, said gas filter comprising a housing and containing an ingredient gas having an absorption spectrum band that nearly corresponds to that of an ingredient gas to be measured or an ingredient to be measured.
  • an absorption type gas analyzer provided with a light source, a cell and a detector
  • a beam of light from the light source is passed through the gas filter filled with a gas having an absorption spectrum band nearly equivalent to an absorption spectrum band of the ingredient gas to be measured or the ingredient in the sample gas, the concentration of which is to be measured.
  • an ingredient gas having higher concentrations in the sample gas can be measured with high accuracy by means of an absorption type gas analyzer having a cell length suitable for measuring the concentration of the ingredient gas when having lower concentrations without changing the cell length.
  • the problem of changing the cell-length in correspondence to the concentration of the ingredient gas in the sample gas is overcome. That is to say, a wide range of concentrations to be measured from lower concentrations to higher concentrations, of the ingredient gas can be measured with high accuracy by means of cells having the same length by merely changing the concentration of the gas enclosed in the gas filter.
  • FIG. 1 is a diagrammatic sectional view showing a preferred embodiment of the present invention
  • FIG. 2 is a graph showing the relation between the output of a conventional absorption type gas analyzer and the concentration of an ingredient gas to be measured in the sample gas;
  • FIG. 3 is a graph showing the relation between the output of an absorption type gas analyzer according to the present invention and the concentration of an ingredient gas to be measured in the sample gas;
  • FIG. 4 is a graph showing the relation between the concentration of CO 2 enclosed in a gas filter and a calibration curve.
  • reference numeral 1 designates a reference cell filled with a gas, such as N 2 , which does not absorb infrared rays.
  • a sample cell 2 is supplied with a sample gas.
  • Light sources 3a, 3b are arranged on one side of the reference cell 1 and the sample cell 2, respectively. Beams of light radiating from these light sources 3a, 3b are transmitted as to intermittent beams after passing through a rotating sector 4, the intermittent beams in turn passing through the reference cell 1 and the sample cell 2, respectively, to alternately enter a condenser microphone 5 arranged on the other side of the reference cell 1 and the sample cell 2 as a detector.
  • Reference numeral 6 designates a condenser film and reference numeral 7 designates a fixed pole.
  • a gas filter 8 is arranged between the reference cell 1 and the sample cell 2 and the condenser microphone 5.
  • a gas having an absorption spectrum band nearly equivalent to that of an ingredient gas, the concentration of which is to be measured, or an ingredient, the concentration of which is to be measured, is enclosed in the gas filter 8.
  • the ingredient, the concentration of which is to be measured is a stable gas such as CO or CO 2
  • the gas filter 8 enclosed the ingredient gas.
  • the ingredient, the concentration of which is to be measured is unstable, e.g. cyan gas
  • the gas filter 8 can be used with an acetylene gas loading having an absorption spectrum band nearly equivalent to that of the ingredient gas.
  • Reference numeral 9 designates an amplifier.
  • infrared rays emitted from the light source 3a are not absorbed in the reference cell 1 but pass through the gas filter 8 to be absorbed in amounts corresponding to the concentration of the gas in the gas filter 8, whereby the condenser film 6 is dislocated.
  • infrared rays emanating from the light source 3b are absorbed in the sample cell 2 in amounts corresponding to the concentration of the ingredient gas contained in the sample gas which is to be measured and pass through the gas filter 8 to be absorbed again, and then the infrared rays enter the condenser microphone 5 to dislocate the condenser film 6.
  • the concentration of the ingredient gas contained in the sample gas is measured from a difference in the dislocation of the condenser film 6.
  • a gas of higher concentration of gas is enclosed in said gas filter 8 when the concentration of the ingredient gas in the sample gas, which is to be measured, is higher while a lower concentration of gas is enclosed in the gas filter 8 when the concentration of the ingredient gas in the sample gas is lower.
  • the cell-length is 10 mm and the ingredient gas, the concentration of which is to be measured, is CO 2
  • CO 2 gas having a concentration of 5% by volume is enclosed in the gas filter 8 in a case of a full scale of 20% by volume (for use in a higher-concentration measurement)
  • CO 2 gas having a concentration of 3% by volume in a case of a full scale of 15% by volume for use in a middle-concentration measurement
  • CO 2 gas is not enclosed in the gas filter 8 in a case of a full scale smaller than several % by volume (for use in a superlower-concentration measurement).
  • the concentration of the ingredient gas to be measured in a sample gas is unknown, it can be initially roughly estimated depending upon the type of sample gas, such as air, smoke from a plant or exhaust gas from a motorcar, so that the concentration of the gas to be enclosed in the gas filter may be selected in correspondence to the estimated concentration.
  • FIG. 4 is a graph showing a relation between a concentration of CO 2 (one example of an ingredient gas to be measured) enclosed in a gas filter 8 and calibration curves as shown in FIGS. 2, 3. More specifically, a ratio of B to A, that is to say B/A ⁇ 100 (%), as shown in FIGS. 2, 3 is plotted along the ordinate while the concentration (Vol %) of CO 2 enclosed in the gas filter 8 is plotted along the abscissa. And, referring to FIG. 4, a point P shows a bending extent of the calibration curve at a 50%-full scale point in FIG. 2 (B/A ⁇ 100 ⁇ 30%) while a point Q shows a bending extent of the calibration curve at a 50%-full scale point in FIG. 3 (B/A ⁇ 100 ⁇ 20%).
  • the bending extent of the calibration curve increases (the linearity is lowered) with an increase in the concentration of the ingredient gas in the sample gas.
  • the bending extent of the calibration curve is reduced with an increase in the concentration of the gas enclosed in the gas filter 8 (but an output is reduced). Accordingly, as described above, when the concentration of the ingredient gas in the sample gas is higher, a gas also having a higher concentration is enclosed in the gas filter 8 while when the concentration of the ingredient gas to be measured in the sample gas is lower, the same gas but having a lower concentration is enclosed in the gas filter. In fact, it is desirable that said concentration of the gas to be enclosed in the gas filter 8 be set so that the bending extent (B/A ⁇ 100) of the calibration curve is 20% or less and the reduction of the output is not increased.
  • the accuracy of measurement is improved by setting the concentration of the gas enclosed in the gas filter 8 at an amount corresponding to the concentration of the ingredient gas contained in the sample gas.
  • CO 2 of which the concentration in a sample gas can be comparatively large, which up until now had to be measured with a short cell, can now be measured with high accuracy without changing the cell length by using an infrared ray analyzer for use in the determination of CO having lower concentrations, in which a cell is formed having a comparatively large length, and providing a gas filter in the optical path of the infrared ray analyzer.
  • a condenser microphone is used as a detector in the above-described preferred embodiment
  • optional detectors such as a solid state detector using a pyroelectric detector, a semiconductor detector, a thermopile and the like may be used.
  • the present invention may be applied to a "fluid-modulation type analyzer" in which a pair of cells are alternately supplied with a reference gas and a sample gas or a single cell is alternately supplied with a reference gas and a sample gas.
  • the gas filter 8 can be constructed as an integrated unit with the detector 5.
  • the gas filter 8 may be arranged between the rotating sector 4 and the reference cell 1 and the sample cell 2.
  • ingredient gas, and the like may be enclosed in a housing surrounding the light source to form the gas filter.

Landscapes

  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
US06/935,301 1985-11-27 1986-11-26 Absorption analyzer Expired - Fee Related US4794255A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP60267640A JPS62126329A (ja) 1985-11-27 1985-11-27 吸光分析計
JP60-267640 1985-11-27

Publications (1)

Publication Number Publication Date
US4794255A true US4794255A (en) 1988-12-27

Family

ID=17447477

Family Applications (1)

Application Number Title Priority Date Filing Date
US06/935,301 Expired - Fee Related US4794255A (en) 1985-11-27 1986-11-26 Absorption analyzer

Country Status (4)

Country Link
US (1) US4794255A (fr)
EP (1) EP0226855B1 (fr)
JP (1) JPS62126329A (fr)
DE (1) DE3650094T2 (fr)

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4885469A (en) * 1987-06-10 1989-12-05 Horiba Ltd. Infrared gas analyzer
US5003175A (en) * 1988-06-01 1991-03-26 Hartmann & Braun Ag Calibration of nondispersive infrared photometer
US5429805A (en) * 1993-01-08 1995-07-04 Fuji Electric Co., Ltd. Non-dispersive infrared gas analyzer including gas-filled radiation source
US5473161A (en) * 1994-06-21 1995-12-05 The Coca-Cola Company Method for testing carbonation loss from beverage bottles using IR spectroscopy
US5572032A (en) * 1993-11-20 1996-11-05 Horiba, Ltd. Gas analyzer and gas-analyzing mechanism
US5764354A (en) * 1995-12-20 1998-06-09 Siemens Aktiengesellschaft Two-beam gas analyzer and method for calibrating a two-beam gas analyzer
US5900635A (en) * 1995-09-29 1999-05-04 Instrumentarium Oy Correction of collision broadening in non-dispersive absorption measurement of gases
GB2358245A (en) * 1999-10-21 2001-07-18 Pittway Corp Photo-acoustic gas sensor
US20030218750A1 (en) * 2002-02-28 2003-11-27 Friberg Stephen R Laser-based spectrometer for use with pulsed and unstable wavelength laser sources
US20050173635A1 (en) * 2004-02-09 2005-08-11 Smith Patrick G. Gas detector
US7034943B1 (en) * 2000-03-03 2006-04-25 Aritron Intrumente AG Gas sensors
US20080277586A1 (en) * 2007-05-07 2008-11-13 Dennis Cardinale Low-Power Fast Infrared Gas Sensor, Hand Held Gas Leak Detector, and Gas Monitor Utilizing Absorptive-Photo-Acoustic Detection
US20100129157A1 (en) * 2003-01-07 2010-05-27 Micropyretics Heaters International, Inc. Heating and sterilizing apparatus and method of using same
CN120334165A (zh) * 2025-06-17 2025-07-18 西安德创电气科技有限公司 一种红外气体分析仪

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE8905226U1 (de) * 1989-04-25 1990-06-13 Siemens AG, 1000 Berlin und 8000 München Nichtdispersiver Infrarot-Gasanalysator
US6067840A (en) * 1997-08-04 2000-05-30 Texas Instruments Incorporated Method and apparatus for infrared sensing of gas
US20120330568A1 (en) * 2010-02-16 2012-12-27 Hamamatsu Photonics K.K. Gas concentration calculation device, gas concentration measurement module, and light detector
DE102011109000B4 (de) 2011-07-29 2014-05-15 Abb Technology Ag Optische Gasanalysatoreinrichtung mit Mitteln zumVerbessern des Dynamikbereichs der Messung

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS4925349A (fr) * 1972-07-03 1974-03-06
US4271124A (en) * 1978-02-24 1981-06-02 Siemens Aktiengesellschaft Non-dispersive infrared gas analyzer for testing gases containing water-vapor
US4297577A (en) * 1978-11-29 1981-10-27 Land Pyrometers Limited Radiation detection of gas compositions
JPS5923380A (ja) * 1982-07-29 1984-02-06 富士通株式会社 デイスプレ−制御方式
US4514635A (en) * 1981-11-26 1985-04-30 Horiba, Ltd. Non-dispersive infrared analyzer

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB849983A (en) * 1956-08-18 1960-09-28 Hartmann & Braun Ag Method and apparatus for the analysis by radiation of mixtures of gases and/or vapours
FR2219723A5 (fr) * 1973-02-23 1974-09-20 Veillard Camille
DE3200128C2 (de) * 1982-01-05 1987-03-26 Georgij Trofimovič Moskva Lebedev Vorrichtung zur Analyse von Gas-Luft-Gemischen

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS4925349A (fr) * 1972-07-03 1974-03-06
US4271124A (en) * 1978-02-24 1981-06-02 Siemens Aktiengesellschaft Non-dispersive infrared gas analyzer for testing gases containing water-vapor
US4297577A (en) * 1978-11-29 1981-10-27 Land Pyrometers Limited Radiation detection of gas compositions
US4514635A (en) * 1981-11-26 1985-04-30 Horiba, Ltd. Non-dispersive infrared analyzer
JPS5923380A (ja) * 1982-07-29 1984-02-06 富士通株式会社 デイスプレ−制御方式

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4885469A (en) * 1987-06-10 1989-12-05 Horiba Ltd. Infrared gas analyzer
US5003175A (en) * 1988-06-01 1991-03-26 Hartmann & Braun Ag Calibration of nondispersive infrared photometer
US5429805A (en) * 1993-01-08 1995-07-04 Fuji Electric Co., Ltd. Non-dispersive infrared gas analyzer including gas-filled radiation source
US5572032A (en) * 1993-11-20 1996-11-05 Horiba, Ltd. Gas analyzer and gas-analyzing mechanism
US5473161A (en) * 1994-06-21 1995-12-05 The Coca-Cola Company Method for testing carbonation loss from beverage bottles using IR spectroscopy
US5900635A (en) * 1995-09-29 1999-05-04 Instrumentarium Oy Correction of collision broadening in non-dispersive absorption measurement of gases
US5764354A (en) * 1995-12-20 1998-06-09 Siemens Aktiengesellschaft Two-beam gas analyzer and method for calibrating a two-beam gas analyzer
GB2358245A (en) * 1999-10-21 2001-07-18 Pittway Corp Photo-acoustic gas sensor
US7034943B1 (en) * 2000-03-03 2006-04-25 Aritron Intrumente AG Gas sensors
US20030218750A1 (en) * 2002-02-28 2003-11-27 Friberg Stephen R Laser-based spectrometer for use with pulsed and unstable wavelength laser sources
US6775001B2 (en) * 2002-02-28 2004-08-10 Lambda Control, Inc. Laser-based spectrometer for use with pulsed and unstable wavelength laser sources
US20100129157A1 (en) * 2003-01-07 2010-05-27 Micropyretics Heaters International, Inc. Heating and sterilizing apparatus and method of using same
US8435459B2 (en) 2003-01-07 2013-05-07 Micropyretics Heaters International, Inc. Heating and sterilizing apparatus and method of using same
US20050173635A1 (en) * 2004-02-09 2005-08-11 Smith Patrick G. Gas detector
US20080277586A1 (en) * 2007-05-07 2008-11-13 Dennis Cardinale Low-Power Fast Infrared Gas Sensor, Hand Held Gas Leak Detector, and Gas Monitor Utilizing Absorptive-Photo-Acoustic Detection
CN120334165A (zh) * 2025-06-17 2025-07-18 西安德创电气科技有限公司 一种红外气体分析仪
CN120334165B (zh) * 2025-06-17 2025-08-26 西安德创电气科技有限公司 一种红外气体分析仪

Also Published As

Publication number Publication date
DE3650094T2 (de) 1995-05-18
EP0226855A2 (fr) 1987-07-01
JPS62126329A (ja) 1987-06-08
EP0226855B1 (fr) 1994-10-12
DE3650094D1 (de) 1994-11-17
EP0226855A3 (en) 1990-01-17

Similar Documents

Publication Publication Date Title
US4794255A (en) Absorption analyzer
CA2381742C (fr) Spectrometre infrarouge utilise pour mesurer des rapports isotopiques
US4271124A (en) Non-dispersive infrared gas analyzer for testing gases containing water-vapor
KR100731864B1 (ko) 레이저 분광 분석 장치
US5689114A (en) Gas analyzing apparatus
JPH102857A (ja) 赤外法によるガス混合物の分析
JP2003501653A (ja) 分析装置
US4692622A (en) Infrared analyzer
US5672874A (en) Infrared oil-concentration meter
US4192996A (en) Measurement of oxygen by differential absorption of UV radiation
US5818598A (en) Nondispersive optical monitor for nitrogen-oxygen compounds
US4247205A (en) Gas measuring apparatus with standardization means, and method therefor
JPS6217183B2 (fr)
US3970387A (en) Nondispersion, two beam, infrared gas analyzer
JPH08247942A (ja) 赤外線ガス分析計
CA1188128A (fr) Detecteur de monoxyde de carbone
US4462686A (en) Laser isotope detection and measurement
GB2070765A (en) Spectrophotometry
JPH0416749A (ja) オゾン濃度測定方法及び装置
US4742229A (en) Pneumatic detector for nondispersive infrared gas analyzers
GB2066947A (en) Gas measuring apparatus with adjustable path length, and method for operation and standardization therefor
JPH07218434A (ja) 赤外線ガス分析計
JPS5876742A (ja) ２光束非分散形赤外線亜硫酸ガス分析方法
JPH0560687A (ja) 赤外分析装置
JPH06281578A (ja) ガス分析計

Legal Events

Date Code Title Description
AS Assignment

Owner name: HORIBA, LTD., 2 MIYANOHIGASHI-MACHI, KISSYOIN, MIN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNORS:MIYATAKE, KIMIO;IMAKI, TAKAO;TAKEDA, KENJI;REEL/FRAME:004636/0922

Effective date: 19861110

Owner name: HORIBA, LTD., JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MIYATAKE, KIMIO;IMAKI, TAKAO;TAKEDA, KENJI;REEL/FRAME:004636/0922

Effective date: 19861110

FEPP Fee payment procedure

Free format text: PAYER NUMBER DE-ASSIGNED (ORIGINAL EVENT CODE: RMPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

Free format text: PAYOR NUMBER ASSIGNED (ORIGINAL EVENT CODE: ASPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

FPAY Fee payment

Year of fee payment: 4

FPAY Fee payment

Year of fee payment: 8

REMI Maintenance fee reminder mailed
LAPS Lapse for failure to pay maintenance fees
FP Lapsed due to failure to pay maintenance fee

Effective date: 20001227

STCH Information on status: patent discontinuation

Free format text: PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362